Swift: Order of execution, rest API - ios

Question

I need some help with my school project.
Why is print(segueShouldOccur) printed before doAPI().
When I actually call doApi() before the print(seagueShouldOccur).
I'm talking about the method: shouldPerformSegue.
The Rest Api does work (already tested).
class ViewController: UIViewController {
var loginArr = [String]()
#IBOutlet weak var _output: UILabel!
#IBOutlet weak var _username: UITextField!
#IBOutlet weak var _password: UITextField!
#IBAction func doLogin(_ sender: Any) {
loginArr.removeAll()
let username = _username.text;
let password = _password.text;
loginArr.append(username!);
loginArr.append(password!);
self._output.text = username;
}
func doApi() -> Bool{
let headers = [
"cache-control": "no-cache",
"postman-token": "6f8a-12c6-87a1-ac0f25d6385a"
]
let url = "https://projects2018.sz-ybbs.ac.at/~szmed/indyapp/indyapi.php?func=0&user=" + _username.text! + "&pass=" + _password.text!
let request = NSMutableURLRequest(url: NSURL(string: url)! as URL,
cachePolicy: .useProtocolCachePolicy,
timeoutInterval: 10.0)
var check = false;
request.httpMethod = "GET"
request.allHTTPHeaderFields = headers
let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
if error == nil && data != nil {
do {
let json = try JSONSerialization.jsonObject(with: data!, options: JSONSerialization.ReadingOptions.mutableContainers) as! [String:AnyObject]
//do your stuff
print(json);
check = true;
} catch {
}
}
else if error != nil
{
}
}).resume()
return check;
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let DashboardC = segue.destination as! DashboardController
DashboardC.receivedStringArr = loginArr
}
override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
if identifier == "performSegueLogin" { // you define it in the storyboard (click on the segue, then Attributes' inspector > Identifier
var segueShouldOccur = doApi()
if (!segueShouldOccur){
print("1 - false");
print(segueShouldOccur);
return false;
}else{
print("2 - true");
print(segueShouldOccur);
return true;
}
}
return false;
}
}

Answer 1

session.dataTask is asynchronous. If you want to know when your api call has completed, you can use completion handler like this :
func doApi(completion : #escaping (Bool?,Error?) -> ()) {
let headers = [
"cache-control": "no-cache",
"postman-token": "6f8a-12c6-87a1-ac0f25d6385a"
]
let url = "https://projects2018.sz-ybbs.ac.at/~szmed/indyapp/indyapi.php?func=0&user=" + _username.text! + "&pass=" + _password.text!
let request = NSMutableURLRequest(url: NSURL(string: url)! as URL,
cachePolicy: .useProtocolCachePolicy,
timeoutInterval: 10.0)
var check = false;
request.httpMethod = "GET"
request.allHTTPHeaderFields = headers
let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
if error == nil && data != nil {
do {
let json = try JSONSerialization.jsonObject(with: data!, options: JSONSerialization.ReadingOptions.mutableContainers) as! [String:AnyObject]
//do your stuff
print(json);
check = true;
} catch {
}
completion(true,nil)
}
else if error != nil
{
completion(false,error)
}
}).resume()
return check;
}
then you can call your function like this :
doApi { (isSuccess, errorMessage) in
if isSuccess {
// perform your operations
} else {
print(errorMessage?.localizedDescription ?? "Some error occured")
}
}